Table 3-3. Weather Radar Return Levels
EHSI Amber Caution or Failure Annunciations (fig.
(1) Same compass source or navigation source.
When both the pilot and copilot select the same compass
or navigation source, the source annunciators will be
(2) Cross-switched navigation sources. If the
pilot selects the copilot's navigation source (VOR2) or if
the copilot selects the pilot's navigation source (VOR1),
the annunciator will be amber to indicate cross-switched
navigation sources. If both the pilot and copilot select
annunciated in amber.
(3) DME hold. When DME is set in the hold
position, an amber H is displayed to the left of the
numerical DME readout
(4) Waypoint annunciations. An amber WPT
annunciation from the long range navigation system (INS)
is displayed to indicate waypoint passage.
(5) Cautions due to failures of DME, GSPD, or
TTG. When distance measuring equipment (DME),
groundspeed (GSPD), or time-to-go (TG) systems fail, the
digital displays will be replaced by amber dashes. If
NAV1 distance information is not available due to TACAN
selection, an amber N/A will appear in the distance
If one pilot selects TCN but the other pilot
selects NAV1 navigation source, the pilot with
the NAV1 data will have an N/A in the distance
display. If TCN is deselected, distance data will
return to the NAV1 distance display.
(6) Target alerts. Weather radar target alerts are
annunciated on the EHSI. A green TGT annunciation
indicates an armed condition, while an amber TGT
indicates an alert condition.
(7) Course select and heading select. Failure of
course or heading select signals will cause these displays
to be replaced by amber dashes. They are also dashed
when the heading display is invalid.
(8) Weather radar failure. Failure of the weather
radar system is indicated on the EHSI by WX FAILURE
EHSI Red failure annunciations (fig. 3-19).
(1) Heading failure. A. failure of the heading
system results in the removal of bearing annunciators,
bearing pointers, course deviation pointer, and course
scale. The digital course readout and digital heading
readout will be dashed, and a red HDG FAIL will be
(2) Course deviation or glideslope deviation
failure. Failure of course or glideslope deviation systems
will result in the removal of course and glideslope pointers
and a red X will be drawn through the scale. The letter G
will appear at the zero deviation position of the glideslope
scale to identify the invalid information
EADI AND EHSI COMPOSITE DISPLAY.
If an EADI or EHSI display unit fails, a composite attitude
and navigation format (fig. 3-20), may be displayed on
the remaining display. Selection of the composite mode
is made by turning the applicable DIM control to OFF. As
in normal EADI and EHSI presentations, all elements are
not displayed at the same time. The presence or absence
of each display element is determined by flight phase,
navigation radio tuning, selected flight director mode,
absolute altitude, etc. The failure, caution, and warning
annunciations function is much the same as for the
normal display mode.